Sleeping Bag Rating Calculator
Sleeping bag comfort and limit from night low.
What it does
Sleeping bags rate colder than comfort, and sleepers vary more than bags. An average sleeper facing 30 F needs a 20 F comfort bag with a 5 F limit, while a cold sleeper needs 15 F comfort and a warm sleeper manages 25. Buffer by body, not bravery.
The tool above applies sleeper buffers with ISO concepts attached. Enter the expected low, pick cold/average/warm, and it prints comfort rating, limit rating, and Celsius comfort. Defaults give 20 F with 5 F limit; cold sleepers at 20 F lows need 5 F bags.
Standards frame the vocabulary. ISO 23537 specifies thermal requirements for adult sport bags at limits above -20 C with comfort/limit/extreme concepts, while the 15/10/5 buffers here are labeled planning margins on top. Limit suits experienced users curled up, never comfort.
Systems keep sleepers warm beyond ratings. Pads block ground cold, tents cut wind, food fuels furnaces, and dry layers beat damp ones. Buy comfort for the forecast low, then manage the rest of the system.
How to use
- Enter the expected night low in F.
- Pick cold, average, or warm sleeper.
- Read comfort rating first.
- Read limit rating.
- Buy at/above comfort.
- Pad and tent for the rest.
Formula
- low
- Expected night low in F, -60 to 100.
- sleeper
- Cold 15, average 10, warm 5 F buffer.
ISO 23537 frames comfort/limit concepts for adult bags; 15/10/5 buffers and the 15 gap are labeled calculator margins.
Worked example
Example: 30 F night
Defaults: 30 F low, average sleeper.
- Inputs: 30 F expected low, average sleeper.
- Buffer: average sleepers take 10 F.
- Comfort: 30 minus 10 = 20 F.
- Limit: 20 minus 15 = 5 F.
- Celsius: -7 C. Tool shows 20 F comfort, 5 F limit.
Reference table
| Low / Sleeper | Comfort | Limit |
|---|---|---|
| 50 / warm | 45 | 30 |
| 40 / average | 30 | 15 |
| 30 / average | 20 | 5 |
| 30 / cold | 15 | 0 |
| 20 / cold | 5 | -10 |
Limits
- Planning margins, not lab ratings.
- Individual variation is large.
- Pads/tents/clothing excluded from math.
- Kids and expeditions excluded.
Common mistakes
- Buying limit rating for comfort.
- Ignoring sleeper type differences.
- Skipping pads under bags.
- Cotton layers in cold.
- Trusting survival ratings for sleep.
Try it yourself
Quick checks. Answers sit tucked under each question.
40 F low, warm sleeper?
Buffer 5. Comfort 40 minus 5 = 35 F. Limit 35 minus 15 = 20 F. Celsius 2 C.
20 F low, cold sleeper?
Buffer 15. Comfort 20 minus 15 = 5 F. Limit 5 minus 15 = -10 F. Celsius -15 C.
Questions
How is comfort rating figured?
Low minus sleeper buffer (cold 15, average 10, warm 5). Here 30-10 = 20 F comfort.
How is the limit rating figured?
Comfort minus 15 F for experienced users curled up. Here 5 F, not for comfort.
What do comfort/limit mean?
ISO 23537 concepts: comfort for standard users, limit lower, extreme survival only.
Do cold sleepers need more bag?
Yes. Cold sleepers add 15 F of bag; warm sleepers add 5.
Does anything else keep me warm?
Yes. Pads, tents, clothing, food, and wind shift real warmth a lot.
What does ISO cover?
Yes. Bags at/above -20 C with adult sport use; kids and expeditions excluded.